1. Field of the Invention
The present invention relates generally to aerosol generators and, more particularly, to vapor driven aerosol generators. The aerosol generators of the invention are able to generate aerosols without requiring the use of compressed gas propellants. The present invention also relates to methods for generating an aerosol. The present invention has particular applicability to the generation of aerosols containing medicated material.
2. Description of the Related Art
Aerosols are gaseous suspensions of fine solid or liquid particles and are useful in a wide variety of applications. For example, medicated liquids and powders may be administered in aerosol form. Such medicated aerosols include, for example, materials which are useful in the treatment of respiratory ailments, in which case the aerosols may be inhaled into a patient""s lungs. Aerosols may also be used in non-medicinal applications including, for example, dispensing air fresheners and insecticides and delivering paints and/or lubricants.
In aerosol inhalation applications, it is typically desirable to provide an aerosol having an average mass median particle diameter of less than 2 microns to facilitate deep lung penetration. Most known aerosol generators are incapable of generating aerosols having an average mass median particle diameter less than 2 microns. Also, in certain applications, it is generally desirable to deliver medicated material at high flow rates, for example, above 1 mg per second. Most known aerosol generators suited for delivering medicated material are incapable of delivering material at such high flow rates while maintaining a suitable average mass median particle diameter. In addition, most known aerosol generators deliver an imprecise amount of aerosol compared with the amount of aerosol that is intended to be delivered.
The related art discloses aerosol generators which employ various techniques for delivering an aerosol. A particularly useful technique involves volatilizing a fluid and ejecting the volatilized fluid into the atmosphere. The volatilized fluid subsequently condenses, thereby forming an aerosol. See, for example, commonly assigned U.S. Pat. No. 5,743,251, the entire contents of which document are hereby incorporated by reference. Such aerosol generators may eliminate or conspicuously reduce some or all of the aforementioned problems associated with the known aerosol generators. However, since these aerosol generators employ heat-generating systems, heat resistive material and, in some cases, various control devices, pumps and valves, the manufacture and assembly of such aerosol generators can be complicated and expensive.
In light of the foregoing, there exists a need in the art for the provision of an aerosol generator which overcomes or conspicuously ameliorates the above described shortcomings in the related art. Accordingly, it is an object of the present invention to provide a vapor driven aerosol generator which produces an aerosol from a fluid by volatilizing the fluid and directing the volatilized fluid therefrom.
Other objects and aspects of the present invention will become apparent to one of ordinary skill in the art upon review of the specification, drawings and claims appended hereto.
The invention provides an aerosol generator which includes a fluid passage having an upstream and a downstream end, a heater arranged to heat fluid in the passage into a gaseous state, a fluid supply arranged to provide a fluid to the upstream end of the passage, a preheater located between the fluid supply and the main heater, the preheater including a heating element which heats a portion of the fluid in the passage into a gaseous state such that fluid in the passage downstream of the heating element is driven through the passage in a downstream direction.
The heating element is preferably located in a chamber having a predetermined volume and/or the fluid supply includes a valve which closes the passage when the heating element heats the fluid into a gaseous state. If desired, the heating element can be located along an inner wall of a metering chamber, the metering chamber being sized to receive a predetermined volume of fluid to be emitted as an aerosol from the aerosol generator. The passage can be located in an organic or inorganic material selected from one or more polymer, metal and ceramic materials. For instance, the passage can be located in a ceramic laminate wherein the passage is defined by a recess in a surface of a first ceramic layer and a surface of a second ceramic layer bonded to the first ceramic layer. The heating element can comprise a layer of resistance heating material located along one or more walls of the passage.